I've always gone to see Reuben at TuningWerkes which is based in South Croydon. It's on the road leading towards the South Croydon Bus Garage/Purley. On the main road there's an Esso Petrol Station, you turn into a road right next to it and it'll be on your right.
Good guys and highly recommended from members in MKIV, ClubPolo & Edition38. They've got there own section in ED38 as well.
http://www.tuningwerkes.com/